1. Field of the Invention
The present invention relates to cosmetic brushes composed of natural bristles (animal hair), which have excellent antimicrobial and deodorant properties and wash-durable antimicrobial properties, and to methods of producing the same.
Furthermore, the present invention relates to cosmetic brushes composed of natural bristles, which use cationic surfactants selected from alkyl ammonium salts or alkylbenzyl ammonium salts containing quaternary ammonium salts and alkyl pyridinium salts, exhibit excellent halo effect and have excellent antimicrobial and deodorant properties and wash-durable antimicrobial properties, and to methods for producing the same.
2. Description of the Related Art
Today, the demand for so-called antimicrobial articles in every field is high as a result of the reflection of hygiene-oriented tendency in society and at home.
Among household articles, consumer demand for antimicrobial properties in toothbrushes is particularly high because toothbrushes are used in the mouth and stored in a moist condition in which bacteria readily grow. Accordingly, a large number of techniques have conventionally been disclosed for antimicrobial toothbrushes. Typical examples are toothbrushes which are treated with surfactants or disinfectants having antimicrobial properties. Examples include an antimicrobial-durable toothbrush which is treated with a solvent solution of disinfectant such as trichlorocarbanilide containing a small amount of lipophilic nonionic surfactant (Japanese Patent Publication No. S48-27389) and a self-sterilizing toothbrush into which a disinfectant such as halogenated salicylanilide and trichlorocarbanilide is permeated (Japanese Utility Model No. S48-31719; Japanese Utility Model No. S50-40688).
Further, reflecting the hygiene-oriented and beauty-oriented tendency of consumers, the demand for antimicrobial properties is also naturally high in hairbrushes, cosmetic brushes and the like other than toothbrushes, in which dandruff, skin dirt or skin oil tends to remain adhered, and all sorts of airborne germs grow and generate molds and unpleasant odors, which create an unhygienic condition. However, surprisingly very few techniques regarding antimicrobial or sterile brushes of such kind have been disclosed. Among the few are a method of rendering antimicrobial properties to natural bristle brushes by adding styrene glycol to a solution of an antimicrobial agent such as isopropylmethyl phenol (Japanese Patent Application Laid-open No. S53-128451) and a method of enhancing antimicrobial properties by treating natural bristles with a phenol antimicrobial agent solution under pressure to permeate the antimicrobial agent into the inside of the bristles (Japanese Patent Application Laid-open No. H03-289905).
On the other hand, research into improving antimicrobial agents for brushes have progressed and antimicrobial agents having excellent antibacterial activity and durability have become usable. For example, a method in which natural bristles are cationized with a cationizing agent having two or more quaternary ammonium groups in a molecule and reacted with an amphoteric or anionic disinfectant (Japanese Patent Application Laid-open No. H02-274205), a method in which a benzimidazole compound and a pyridine compound are used in combination as an antimicrobial agent (Japanese Patent Application Laid-open No. H05-7510), and a method in which use of a quaternary ammonium salt as a disinfectant is suggested (Registered Japanese Utility Model No. 3019605: Heisei 7; Registered Japanese Utility Model No. 3063570: Heisei 11) have been disclosed.
However, in the prior art described above, antimicrobial efficacy by antimicrobial agents is excellent in the early stage of treatment but it is substantially insufficient. As a result, the brush body and natural bristles become blackish due to the growth of bacteria and molds and generation of unpleasant odor cannot be completely prevented. Furthermore, the antibacterial agents gradually fall out and the antimicrobial property is not durable and shortly disappears, which does not fully satisfy consumer need.
In general, in order to remove remaining cosmetic agents after each use, cosmetic brushes are always washed with water or hand-washed with rubbing after use. Therefore, high wash-durability is required. To satisfy this requirement, a binder was conventionally used to increase wash-durability, which caused a rough feel to the skin and was not accepted by consumers.
Among the abovementioned known techniques, the most frequently used method for the treatment of natural bristles is a method in which the natural bristles are submerged in a solution of commonly used antimicrobial agent, and after solvent removal, the bristles are dried to immobilize the antimicrobial agent or disinfectant. However, in this method, particularly in cosmetic brushes, the tip of the natural bristles hardened because of physical changes caused by the antimicrobial agent, resulting in disadvantages in use, such as roughness of the cosmetic brush to the skin and poor retention of cosmetic agents on the cosmetic brushes.
Further, conventionally, even when common quaternary ammonium salts were used, the antimicrobial agents did not sufficiently adhere onto natural bristles and unpleasant natural bristle odor could not be prevented, retention of antimicrobial properties after washing (i.e., wash-durability) was poor, and the halo width, i.e., an index for antimicrobial efficacy, was insufficient.
The present invention relates to brushes, particularly cosmetic brushes which are highly demanded reflecting the current fashion-oriented, aesthetic requirement. The present invention intends to solve the abovementioned problem and provide a cosmetic brush characterized in that it is markedly antimicrobial, the retention of the antimicrobial properties is long, it has no natural bristle odor, the use of insecticide is not necessary because it has insecticidal effect, and further hardening of the tip of the natural bristles due to physical changes caused by antimicrobial agents does not occur, which results in smoothness to the skin and excellent retention of cosmetic agents on the cosmetic brush.
Accordingly, by directing attention to the utilization of those quaternary ammonium salts used in prior art and more sufficiently adhering antimicrobial agents to natural bristles, an objective of the present invention is to provide a cosmetic brush in which natural bristle odor is prevented, the halo width is sufficient, wash-durability of antimicrobial properties is satisfactory, and further insecticidal effect renders a function as an insecticide.
The halo width used in the present invention is generally known as a standard or an index of antimicrobial properties in antimicrobial articles. In an antimicrobial test, gram-positive and gram-negative bacteria are cultured on an agar medium, an antimicrobial agent diffuses on the agar medium plate, and after cultivation, the area around a test strip of natural bristles, where bacterial growth was inhibited, is measured to numerically express the antimicrobial properties.
The halo width is generally measured in accordance with JIS-L-1902, and represented by the following equation:
W=(Txe2x88x92D)/2 
W: halo width
T: total length of test strip and halo (mm)
D: length of test strip (mm)
In order to solve the abovementioned problem in cosmetic brushes, the present inventors have conducted intensive studies to complete the present invention by using particular quaternary ammonium salts selected from quaternary ammonium salts used as cationic surfactants for treating the cosmetic brushes.
Furthermore, the present inventors have found that among cationic surfactants, alkyl pyridinium salts have similar antimicrobial or disinfectant characteristics.
Namely, the present inventors directed their attention to the affinity of various surfactants having antimicrobial properties to natural bristle proteins. Various surfactants having excellent antimicrobial properties, mainly quaternary ammonium salts, were adsorbed or adhered onto natural bristles and their efficacy was compared. The present inventors, having focused on cationic surfactants which are adsorbed onto natural bristle proteins and are difficult to be removed by washing, found that antimicrobial properties of natural bristles is remarkably improved when alkyl ammonium salts or alkylbenzyl ammonium salts containing a quaternary nitrogen and further, alkyl pyridinium salts, were used, and thus completed the present invention.
The present invention can economically provide an inexpensive cosmetic brush composed of natural bristles which is markedly smooth to the skin, well holds cosmetic agents, has excellent antimicrobial properties, and has long-lasting wash-durable antimicrobial properties, by treating natural bristles in a warm bath containing ammonium salts virtually without changing the shape, appearance or feel of the natural bristles.
Further, the present inventors have succeeded in preventing bacterial odor generation, preventing animal hair odor characteristic to natural bristles, which has been considered to be most difficult, and further improving wash-durability of antimicrobial properties, by using the abovementioned quaternary ammonium salts or alkyl pyridinium salts to sufficiently adhere the antimicrobial agents onto the natural bristles.
In the present invention, a number of quaternary ammonium salts were applied to be adsorbed onto natural bristles and their efficacy was compared. The results revealed that when cationic surfactants, in particular alkyl ammonium salts or alkylbenzyl ammonium salts containing a quaternary nitrogen and alkyl, were used, their adsorption onto the natural bristle protein was high, the antimicrobial properties was hard to remove by washing and well retained and, the feel of the hair tip to the skin was markedly gentle, cosmetic agents were well held, and animal hair odor was prevented, virtually without changing the shape, appearance or feel of the natural bristles, and further, that insecticidal effect was generated so that there was no need to use conventionally used insecticides such as naphthalene.
Further, the present invention revealed that cationic surfactants, alkyl pyridinium salts, were also as effective as the abovementioned quaternary ammonium salts in the same manner as described above.
Furthermore, the present invention is characterized in unique contrivances, such as adsorption of antimicrobial agent in a heated solution and use of an auxiliary agent and a protein denaturation agent as described below.